# CVE-2025-40218: mm/damon/vaddr: do not repeat pte_offset_map_lock() until success

> A local attacker can cause a system soft lockup and denial of service by triggering an infinite loop in the Linux kernel DAMON module during CPU hotplugging.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 4 Dec 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-40218, DEBIAN-CVE-2025-40218, GHSA-349m-qg9r-c9hf, ROOT-OS-UBUNTU-2404-CVE-2025-40218, UBUNTU-CVE-2025-40218

## What is CVE-2025-40218?

CVE-2025-40218 is a denial of service vulnerability in Linux, published on 4 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

mm/damon/vaddr: do not repeat pte_offset_map_lock() until success

DAMON's virtual address space operation set implementation (vaddr) calls
pte_offset_map_lock() inside the page table walk callback function.  This
is for reading and writing page table accessed bits.  If
pte_offset_map_lock() fails, it retries by returning the page table walk
callback function with ACTION_AGAIN.

pte_offset_map_lock() can continuously fail if the target is a pmd
migration entry, though.  Hence it could cause an infinite page table walk
if the migration cannot be done until the page table walk is finished. 
This indeed caused a soft lockup when CPU hotplugging and DAMON were
running in parallel.

Avoid the infinite loop by simply not retrying the page table walk.  DAMON
is promising only a best-effort accuracy, so missing access to such pages
is no problem.

## Which versions are affected by CVE-2025-40218?


## How do I fix CVE-2025-40218?

Apply the vendor's patch.

## Is CVE-2025-40218 being exploited?

There is no known exploitation of CVE-2025-40218 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40218 and fix it if it is affected.

What it is: CVE-2025-40218 is a denial of service vulnerability in Linux, published on 4 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-40218 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-40218/ (Markdown: https://insights.sbomify.com/CVE-2025-40218/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40218
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40218
- OSV: https://osv.dev/vulnerability/CVE-2025-40218

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40218/
Summaries are generated and may contain mistakes; the official description above is the record.